It’s a 34 mm hollow bar that Racing Beat used to offer. The arms were poorly engineered and eventually these arms break on fatigue. RB stopped selling this particular bar for that reason. Drop by if you want to see the remains of one of these…one arm snapped on me while autoxing a few years ago. I thought the differential had broken as the grip on the rear was oscillating from right to left under acceleration. I guess it was because the roll stiffness had became relatively so low in the front that the fast increasing weight transfer in the rear and the resulting loss of grip at the tires was too much for the Torsen differential to handle – just a guess... This weird behavior disappeared once I put back my faithful 1.25” solid ST bar.